ELECTRIC FIELD SENSOR

Abstract: An electric field sensor equipped with a sensor head (1), package (13) housing the head (1), and an antenna (14) attached to the package (13) and connected to the head (1). The head (1) is composed of a substrate (3) and an optical modulator (4) mounted on the substrate (3). The modulator (4) is provided with an input optical waveguide (5) formed on the substrate (3), two phase-shifting optical waveguides (6) branched from the waveguide (5) on the substrate (3) and having the refractive indexes variable depending upon the intensity of the applied electric field, an output waveguide (7) joined with the waveguides (6) on the substrate (3), and two modulating electrodes (8) formed on or in the vicinity of the waveguides (6). The antenna (14) has two rod antenna elements (17 and 18) which are extended in parallel with the waveguide (6) in the opposite directions from the central part of the package (13). It is possible to fix the antenna (14) to the side face (21) of the package (13) and constitute the antenna (14) of two antenna element film pieces (22 and 23) which are extended in parallel with the guides (6) in the opposite directions from the central part of the side face (21). The antenna element film pieces (17 and 18) can be fixed to the substrate (3). It is also possible to form a plurality of optical modulators on the substrate and connect the antennas, respectively, to the modulators.

Description: Technical Field This invention relates to an electric field sensor for measuring an electric field intensity of an electromagnetic wave or the like. Background Art Fig. 1 shows a conventional electric field sensor. The electric field sensor comprises a sensor head 1 and an antenna 2 connected to the sensor head 1. The sensor head 1 has a substrate 3 and an optical modulator 4 attached to the substrate 3. The optical modulator 4 comprises an incident optical waveguide 5 formed on the substrate 3, two phase-shift optical waveguides 6 which are formed on the substrate 3 to be branched from the incident optical waveguide 5 and each of which has a variable refractive index varying in response to an electric field intensity applied thereto, an outgoing optical waveguide 7 formed on the substrate 3 to join the phase-shift optical waveguides 6, and two modulation electrodes 8 formed on or in the vicinity of the phase-shift optical waveguides 6. The incident optical waveguide 5 is connected to an incident optical fiber 9. The outgoing optical waveguide 7 is connected to an outgoing optical fiber 10. The antenna 2 has two rod antenna elements 11. The rod antenna elements 11 are connected through lead wires 12 to the modulation electrodes 8, respectively. The rod antenna elements 11 are arranged to face a direction of an electric field, in other words, to be perpendicular to the phase-shift optical waveguides 6. The rod antenna elements 11 are fixed to a package which is not illustrated in the figure. In the conventional electric field sensor, the antenna elements face the direction of the electric field during measurement. Accordingly, a draw-out portion of the optical fiber faces a direction of measurement. This possibly results in a damage of the optical fiber. In the conventional electric field sensor, the antenna must be arranged in various directions during measurement because of its strict directivity. From US-patent 5,210,407 an electric field sensor according to the preamble of claim 1 is known having a pair of opposing plates forming a capacitor type antenna arrangement. According to the known electric field sensor the two antenna elements extend in the same direction to each other perpendicularly to the direction of the phase shift optical waveguides. Disclosure of the invention It is an object of this invention to provide an electric field sensor capable of preventing a damage of an optical fiber. This object is solved by an electric field sensor having the features of the independent claim 1. Preferred developments of the invention are given in the dependent claims. Brief Description of the Drawing Fig. 1 is a perspective view of a conventional electric field sensor. Fig. 2 is a plan view of one embodiment of this invention. Fig. 3 is a perspective view of another embodiment of this invention. Fig. 4 is a plan view of still another embodiment of this invention. Fig. 5 is a plan view of a further embodiment of this invention. Fig. 6 is a plan view of an electric field sensor having further antennas Fig. 7 is a side view of the sensor in Fig. 6. Fig. 8 is a perspective view of a further sensor having a plurality of antennas. Embodiments Description will now be made in detail as regards embodiments of this invention with reference to the drawing. As illustrated in Fig. 2, an electric field sensor according to this invention comprises a sensor head 1, a package 13 accommodating the sensor head 1, and' an antenna 14 attached to the outside of the package 13 and connected to the sensor head 1. The sensor head 1 has a substrate 3 and an optical modulator 4 attached to the substrate 3. The optical modulator 4 comprises an incident optical waveguide 5 formed on the substrate 3, two phase-shift optical waveguides 6 which are formed on the substrate 3 to be branched from the incident optical waveguide 5 and each of which has a variable refractive index varying in response to an electric field intensity applied thereto, an outgoing optical waveguide 7 formed on the substrate 3 to join the phase-shift optical waveguides 6, and two modulation electrodes 8 formed on or in the vicinity of the phase-shift optical waveguides 6. The incident optical waveguide 5 is connected to an incident optical fiber 9. The incident optical fiber 9 is connected to a light source 15. For example, the light source 15 comprises a semiconductor laser. The outgoing optical waveguide 7 is connected to an outgoing optical fiber 10. The outgoing optical fiber 10 is connected to an optical detector 16. The antenna 14 comprises two rod antenna elements 17 and 18. The rod antenna elements 17 and 18 extend in opposite directions with their one ends located at a center portion of the package 13 and are arranged in parallel to the phase-shift optical waveguides 6. The rod antenna elements 17 and 18 are connected through lead' wires 19 and 20 to the modulation electrodes 8, respectively. A light beam from the light source 15 is incident through the incident optical fiber 9 to the incident optical waveguide 5 and branched by the two phase-shift optical waveguides 6 into branched beams which are again combined together in the outgoing optical waveguide 7. The light beam after being combined in the outgoing optical waveguide 7 is emitted through the outgoing optical fiber 10 to the optical detector 16. When the antenna 14 receives a reception signal, the modulation electrodes 8 apply predetermined electric fields to the phase-shift optical waveguides 6. Depending upon the intensities of the electric fields, the refractive indexes of the phase-shift optical waveguides 6 are varied. This results in variation of phases of the light beams transmitted through the phase-shift optical waveguides 6. A more specific example of the electric field sensor illustrated in Fig. 2 will be described hereinafter. The substrate 3 comprises a LiNbO 3 plate. The incident optical waveguide 5, the phase-shift optical waveguides 6, and the outgoing optical waveguide 7 are formed by thermal diffusion of Ti on a Z plane of the substrate 3. The incident optical fiber 9 comprises a constant-polarization optical fiber. Another embodiment illustrated in Fig. 3 has similar components depicted by the same reference numerals as those described in conjunction with the embodiment of Fig. 2. As illustrated in Fig. 3, the antenna 14 has two film antenna elements 22 and 23 fixedly attached to a side surface 21 of the package 13. The film antenna elements 22 and 23 extend in opposite directions with their one ends located at a center portion of the package 13 and are arranged in parallel to the phase-shift optical waveguides 6. The film antenna elements 22 and 23 are connected through lead wires 24 and 25 to the modulation electrodes 8, respectively. With the electric field sensors according to the embodiments illustrated in Figs. 2 and 3, it is possible to prevent a damage of the optical fiber because the draw-out portion of the optical fiber connected to the electric field sensor does not face the direction of measurement. A still another embodiment illustrated in Fig. 4 has similar components depicted by the same reference numerals as those described in conjunction with the embodiment of Fig. 2. As illustrated in Fig. 4, an antenna 26 has two film antenna elements 27 and 28 formed on the substrate 3 in parallel to the phase-shift optical waveguides 6. The film antenna elements 27 and 28 are arranged on both sides of the phase-shift optical waveguides 6. The film antenna elements 27 and 28 are connected through lead wires 29 and 30 to the modulation electrodes, respectively. As illustrated in Fig. 5, the film antenna elements 27 and 28 may be arranged on one side of the phase-shift optical waveguides 6. With the electric field sensor according to the embodiments illustrated in Figs. 4 and 5, it is possible to prevent a damage of the optical fiber because the draw-out portion of the optical fiber connected to the electric field sensor does not face the direction of measurement. The electric field sensor according to the embodiments in Figs. 4 and 5 are adapted to achieve reduction of size. As illustrated in Figs. 6 and 7, an electric field sensor comprises the sensor head 1, the package 13 accommodating the sensor head 1, and antennas 31, 32, and 33 attached to the outside of the package 13 and connected to the sensor head 1. The sensor head 1 comprises a substrate 3 and a plurality of optical modulators 34, 35, and 36 attached to the substrate 3. Each of the optical modulators 34, 35, and 36 has the incident optical waveguide 5 formed on the substrate 3, the two phase-shift optical waveguides 6 which are formed on the substrate 3 to be branched from the incident optical waveguide 5 and each of which has a variable refractive index varying in response to the electric field intensity applied thereto, the outgoing optical waveguide 7 formed on the substrate 3 to join the phase-shift optical waveguides 6, and the two modulation electrodes 8 formed on or in the vicinity of the phase-shift optical waveguides 6. The incident optical waveguide 5 is connected to the incident optical fiber 9. The incident optical fiber 9 is connected to the light source 15. The outgoing optical waveguide 7 is connected to the outgoing optical fiber 10. The outgoing optical fiber 10 is connected to the optical detector 16. The antennas 31, 32, and 33 are arranged to be perpendicular to one another. The antennas 31, 32, and 33 are connected through the lead wires to the modulation electrodes 8 of the optical modulators 34, 35, and 36, respectively. As illustrated in Fig. 8, each of the optical modulators 34, 35, and 36 has the incident optical waveguide 5 formed on the substrate 3, the two phase-shift optical waveguides 6 which are formed on the substrate 3 to be branched from the incident optical waveguide 5 and each of which has a variable refractive index varying in response to the electric field intensity applied thereto, the outgoing optical waveguide 7 formed on the substrate 3 to join the phase-shift optical waveguides 6, and the two modulation electrodes 8 formed on or in the vicinity of the phase-shift optical waveguides 6. The sensor head 1 has a common incident optical waveguide 37 connected to the incident optical fiber 9, primary branch optical waveguides 38 and 39 formed on the substrate 3 to be branched from the common incident optical waveguide 37, secondary branch optical waveguides 40 and 41 formed on the substrate 3 to be branched from the primary branch optical waveguide 38, and tertiary branch optical waveguides 42 and 43 formed on the substrate 3 to be branched from the primary branch optical waveguide 39. The secondary branch optical waveguide 40 is connected to the incident optical waveguide 5 of the optical modulator 34. The secondary branch optical waveguide 41 is connected to the incident optical waveguide 5 of the optical modulator 35. The tertiary branch optical waveguide 42 is connected to the incident optical waveguide 5 of the optical modulator 36. The tertiary branch optical waveguide 43 is connected through the outgoing optical fiber 10 to the optical detector 16. The light beam transmitted through the tertiary branch optical waveguide 43 is emitted through the outgoing optical fiber 10 to the optical detector 16. The light beam transmitted through the tertiary optical waveguide 43 is used as a reference light beam to monitor the light beam transmitted through the optical modulators 34, 35, and 36. Each of the embodiments illustrated in Figs. 6 through 8 has a plurality of antennas. It is therefore unnecessary to change the orientation in various directions during measurement. In addition, it is possible to carry out measurement independent from the incoming direction of the electromagnetic wave to be measured and from the polarization component. Industrial Applicability This invention is adapted for use in a device for measuring an intensity of an electric field such as an electromagnetic wave and electromagnetic noise.

Claims: An electric field sensor comprising: a sensor head (1) having a substrate (3) and an optical modulator (4) attached to said substrate (3), said optical modulator (4) comprising an incident optical waveguide (5) formed on said substrate (3), two phase-shift optical waveguides (6, 6) which are formed on said substrate (3) to be branched from said incident optical waveguide (5) and each of which has a variable refractive index varying in response to an electric field intensity applied thereto, an outgoing optical waveguide (7) formed on said substrate (3) to join said phase-shift optical waveguides (6, 6) and two modulation electrodes (8, 8) formed on and or in the vicinity of said phase-shift optical waveguides (6, 6); a package (13) accommodating said sensor head (1); and an antenna (14, 26) comprising two antenna elements (17, 18, 22, 23, 27, 28) connected to said two modulation electrodes (8, 8), respectively, characterized in that said two antenna elements (17, 18, 22, 23, 27, 28) extend in opposite directions in parallel with said phase-shift optical waveguides (6, 6) with their ends located at a center portion of said package. An electric field sensor according to claim 1, wherein said two antenna elements are rod antenna elements (17, 18) mounted on an outside of said package (13). An electric field sensor according to claim 1, wherein said two antenna elements are film antenna elements (22, 23) formed on an outside surface (21) of said package (13). An electric field sensor according to claim 1, wherein said two antenna elements are film antenna elements (27, 28) formed on said substrate (3). An electric field sensor according to claim 4, wherein said film antenna elements (27, 28) are disposed at opposite sides with reference to said optical modulator (4), respectively. An electric field sensor according to claim 4, wherein said film antenna elements (27, 28) are disposed at the same side with reference to said optical modulator (4).

Inventors: TOKANO YUICHI, TOKANO, YUICHI
Applicants: TOKIN CORP, TOKIN CORPORATION
Application year: 1994
Main classification: G01R15
IPC codes: G01R15, G01R29